1. Field of the Invention
The present invention relates to a motor vehicle steering column switch system having a switch detector, a decoder, and an error identifier in which the switch detector detects the position of a steering column switch lever and converts detected switch positions into corresponding bit patterns, the decoder assigns switch functions to the bit patterns, and the error identifier identifies errors in transmission or reception of the bit patterns.
2. Background Art
Modern steering column switch systems do not control components such as blinkers and windshield wipers by directly switching electrical current to the components. Instead, such systems employ a micro-controller which detects the position of the steering column switch lever based on position signals which are indicative of the switch positions. The micro-controller is used to assign a corresponding switch function (e.g., turn on left blinker, turn off rear windshield wiper, etc.) to each switch position. As such, the micro-controller decodes a position signal to determine the corresponding switch function. The micro-controller transmits appropriate control signals to the control units to carry out the switch function corresponding to the position signal (i.e., the switch function corresponding to the position of the switch lever). The control units then carry out appropriate actions to satisfy the switch function.
Commonly assigned U.S. Pat. No. 6,800,839 discloses an opto-electronic switch position detector for detecting the position of a movable switch. The detector includes a light source, a light shutter, and a plurality of light receivers. The light shutter is connected to the switch to move as the switch moves between different switch positions. As a result, the position of the light shutter relative to the light receivers depends on the switch position. The light shutter is in a different position relative to the light receivers for each switch position. For each switch position, the light shutter blocks the light of the light source from reaching certain ones of the light receivers while enabling the remaining ones of the light receivers to receive the light of the light source. Consequently, a different arrangement of the light receivers receive light of the light source for each switch position. As such, the switch positions are determinable as a function of which light receivers receive light of the light source and which light receivers do not receive light of the light source.
As described, the switch positions respectively correspond to different light receiver arrangements in which some of the light receivers are effectively turned on by receiving light of the light source while the remaining light receivers are effectively turned off by not receiving light of the light source. As such, each light receiver arrangement corresponds to a respective bit pattern (e.g., “1001” which means that the first and fourth ones of the light receivers receive light while the second and third ones of the light receivers do not receive light). Thus, each switch position and its corresponding switch function respectively corresponds to a bit pattern.
Control mechanisms such as current measurements, switching sequence monitoring, error codes, etc., make it possible to recognize errors or defects caused by light conduction path interruptions between the light source and the light receivers (i.e., to recognize errors in the transmission or reception of bit patterns). Such errors result in light receivers not receiving light of the light source during the times that the light receivers are suppose to receive the light of the light source.